2011 Field Notes: July 22

Rock ledge with a more thank 65-foot drop to the ground.

22 July: At least one of our nests has a young eagle yet to fledge! This bird is at least 62 days old and reluctant to leave the safety of the nest. This nest is more than 65 feet from the nearest safe ground, so this youngster may be wise to hang on for a while.

Four eagles fledged last week from three different nests. We caught up with one of the fledglings perched on a large rock outcrop about 100 meters away from its nest. We watched it for about 30 minutes before it took flight!  It flew with strong wingbeats for about 250 meters, then began gliding and landed a bit awkwardly on a sagebrush-covered hillside across the canyon. The bright, white band on the tail and stark, white wing patches were clearly visible to us. Summer is in full swing now, with temperatures in the low-mid 90s most days.

Golden Eagle Posse member Anne Hay filed this report and photograph shortly after the eagle she had been monitoring left the nest:

Fledging flapping its wings on a rock ledge near the nest.

“I was unable to visit the nest until Wednesday morning, and sure enough, the chick had abandoned the nest. The only bird I saw in the nest was a swallow, picking through the nesting material. I began searching, and 23 minutes later I spotted the fledgling standing near the ground on a small rock, west of the nesting area. About an hour after I arrived, the fledgling began calling out loudly. In the past, this usually meant an adult was visible, and sure enough, a parent arrived, dropping a small rabbit for the fledgling to dine on. The fledgling immediately ran to the prey and began mantling it, combined with peeping. The parent only stayed for 3-minutes. The fledgling fed for around 32 minutes, then walked a short distance west, and flopped down flat on the ground with its wings outstretched on either side. YIKES! Am I glad this wasn’t my first sighting of the fledgling! It looked like a dead eaglet! It only laid this way for 6-minutes, then it flapped/jumped onto a low rock in a shady area. It spent some time jumping between rocks in the sun, and rocks in the shade, preening, or looking around. At one point a female grackle began to harass the fledgling. This bird flew around the fledgling, from near-by rock to near-by rock, in two separate sessions, continually calling out. The grackle stayed for 19 minutes the first time, and 18-minutes the second time. Sometimes the fledgling watched it, sometimes it ignored it. Once the grackle flew at the fledgling, and pecked its tail.

Mid-afternoon an adult glides past, traveling north, over the rock formation and out of sight. The fledgling spies it, and begins calling. About 5-minutes later the fledgling begins moving west, first slowly, then faster, then it begins climbing the hill, hopping from rock to rock with some wing flaps until it is at the top of the ridge! From here the fledgling did a lot of looking around, preening, a little wing exercising, as well as a few very short flights along the ridge line. Twice the eaglet walked over the ridge top to the north, and out of my sight, then a short time after again reappeared on the top of the ridge line. I kept waiting for the flight off of the ridge, hoping it wouldn’t be a landing on the highway, but by 4:30, the fledgling still hadn’t taken the big leap. What a fascinating day!

Intern Pat Rodgers collecting prey remains from under one nest.

I’ve just begun to summarize our data from this year and compare with the previous two years. I’ll save details for our peer-reviewed papers, but this year has been quite a departure from 2009 and 2010 in several respects. The number of active nests this year was only about half of the number we’ve seen in each of the last two years, and far fewer of the active nests contained more than one chick. Our nighttime surveys indicate that both jackrabbit and cottontail populations have dropped markedly this year. We will be analyzing all of these findings for the next several weeks, but this study is becoming more and more interesting and stimulating some new questions about the cause of rabbit population fluctuations and the effects of these fluctuations on eagles and other predators. We’re seeing both a drop in the number of breeding eagles and an increase in the number of prey species showing up in the diet. We’re especially interested in finding out how habitat and human activities influence these results and how things will change next year.

I’m also anxious to compare our findings in the Bighorn Basin with a sister study site in Yellowstone’s Northern Range. This is the first year that Golden Eagle nests have been systematically surveyed there, and our colleagues in the Park have found more than twice the number of nest areas than expected!

2011 Field Notes: July 8

Rugged terrain in the Big Horn Basin.

July 8: Summer has definitely arrived in the Bighorn Basin! Still a good deal of green and some wildflowers in bloom, but things are heating up and drying out. It was 93 degrees F. yesterday afternoon when several of us visited one of our successful eagle nests. The single fledgling left the nest more than two weeks ago, at about 54 days of age. She wasn’t quite ready for sustained flight yet, so she stayed in the rocks and sagebrush around the nest for several days before she finally took flight and left the immediate area. In the meantime, both parents continued to bring her freshly-caught prey. Our team began collecting prey remains in and around the nest to determine this family’s nesting food habits in 2011. Next week, I’ll post some photographs of this trip and what we discovered. Nearly all of the nestling eagles in our study area are nearing fledging. We have fewer active nests this year compared with the last two years, and most of our nests have only one chick. However, Bud and Dale Schrickling and Richard Brady and Sharyl McDowell have been monitoring one photogenic nest with 2 chicks. These two successfully left the nest several days ago.  Here are reports from the Shricklings filed June 23 and July 06 along with one of Dale’s fine photographs:

Meal delivery to the nest

June 23: “We had probably the most exciting three hours of this year, if not the total three years we have been monitoring nests. Normally during an observation year you are lucky to observe a single prey delivery. This day we witnessed a total of three deliveries within a three hour period. To make it even more fantastic, Dale got pictures of all three. In addition, Richard Chapman showed up a little while later and did the video interview, which was quite fun to do. He really seems to enjoy doing what he does and seems quite professional at performing it. Our No. 1 chick will be fledging within the next ten days. (our estimate). No. 2 seems to be at least a week if not more behind no. 1.”

July 6: “On 27 June we observed a lot of activity from no. 1 that would indicate she was getting ready to fledge. She would hop about the nest flapping her wings and actually rising above the nest a foot or so. No. 2 would just watch. We estimate that no. 1 is approximately53 -54 days old, where no. 2 is as much as a week younger. On 04 July we returned after a week of absence to find both chicks gone from the nest. On 05 July we went by the nest for a quick check and to see if there were any of the former chicks in the area. We saw one mature eagle do a nest fly-by, but that was all.”

Golden eagle

I was able to visit the nest area yesterday, and observed both new fledglings making good use of shade under a rock outcrop about 100 meters from the nest and one adult watching from the ground nearby – both fledglings looked healthy. Stay tuned for an update next week!

2011 Field Notes: June 22

22 June: It has been an exciting couple of weeks since last entry! The weather continued windy, cool, and rainy/snowy through last week, but has now become more like summer – with drying conditions and warmer temps. The sagebrush-steppe of the Bighorn Basin remains green. Our University of Wyoming, Berry Center for Biodiversity Conservation interns, Patrick Rodgers and Nathan Horton filed an insightful and particularly dramatic report and a photograph of an eagle grasping a pronghorn fawn last week:

“We arrived at the nest on a beautiful and calm morning to find the chick up and about with one of the adults in the nest. The chick still had a mostly white head and chest with wings and back that were an uneven mix of white down and dark feathers (with mostly white down), and a bright yellow cere; we estimated the chick to be 30-35 days old. On this day of observation we learned a very important lesson in pronghorn parenting: never try to conceal your fawn in sagebrush 300 yards from an active golden eagle nest. At 10:15 we observed one of the adult eagles leave the chick in the nest and make a landing 300 yards in front of our vehicle. The landing was not a typical, smooth landing of a golden eagle; rather it was rough with wings spread wide for balance followed shortly by the use of the beak to tear and pull on the prey upon which it had landed. Then, from the nearby draw came at full speed three pronghorn antelope which chased the eagle off of its kill. The eagle came and landed 50 yards from our vehicle atop a telephone pole where it sat a few minutes before slicing and flying off for another attempt to enjoy its recently killed meal. We observed the whole ordeal play out as the two eagles would come to the kill and feed, and the pronghorn would return (an estimated 5 – 8 times) with relentless persistence to try and chase them away. We were both in awe at the fact that this could be a pronghorn kill and waited patiently for a view of the prey, when after about four hours one of the adult eagles drug a bloody and partially eaten pronghorn fawn on top of a large sagebrush. Both eagles fed on the fawn, but we watched one eagle feed till its crop bulged to a softball size projection on its chest, and guard the dead fawn for a little over two hours before we reluctantly left the spectacle before us. It was amazing and inspiring to see the persistence of the pronghorn and the power of the golden eagle, and it was a special reminder of the importance of this keystone species in the invaluable sagebrush steppe of Wyoming.”

It’s a fact of nature that some individuals die so that other individuals live. In this case, the parent eagles in Nest 7 took the life of a newborn pronghorn fawn to support their own family. We’ll be completing our mid-season rabbit surveys this week and should have a better sense about whether the main eagle prey in our study area has remained stable or declined since last year.

2011 Golden Eagle Journal

10 June:  Headed out into Bighorn Basin to check on a few eagle nests and follow up a lead on a Burrowing Owl nest I’d heard about.  Finally a good day for fieldwork, with temperatures in the 60s F, and relatively calm winds.  High clouds, but mostly sunny today.  I’ve never seen the Bighorn Basin so green this time of year . . .or any time of year, for that matter.  Daisies, Indian Paintbrush, and Scarlet Globemallow beginning to bloom, but no sign of Larkspur yet.  My first stop was along the two-track where the Burrowing Owl was reported.  Roads still a bit muddy!  Wow, it was worth coming out here, though.  I spotted the owl near her burrow – no other owls around, and no prairie dogs visible.  This was an active prairie dog colony two years ago, but apparently inactive now – I wonder if sylvatic plague hit this colony?  Several pronghorn around. One doe approached me, and I suspect that she had a newly born fawn nearby.  I backed away after snapping a couple of quick photos with my 500 mm lens.

I was able to visit four Golden Eagle nest sites and confirm that three of them are inactive this year.  The fourth nest has a nestling that is about 40-45 days old!  Overall, it appears that only about 16 of our nest areas are active this year, compared with 30 each in 2009 and 2010.  We’re exploring the possibility that cottontail populations have declined this year.  It will be interesting to see if the eagles that are nesting this year are including more species in their diet, instead of the >90% cottontails we’ve seen the last couple of years. Our Golden Eagle Posse members are monitoring several active nests.  The West Zone Team of Rosemarie Hughes, Anne Hay, Richard Gruber, John Ross, and Don Chaffey filed this report along with a beautiful photograph from nest 43 taken by Anne Hay last week:

“It was a little quieter this week than last.  One constant though was the nestling is sure talkative.  It was very boisterous the first day we were out and little more subdued the second day, even though when an adult was close by it would let us know.  The eaglet is getting darker every time we see it.  It is losing its fluffy white down and you can see it in the nest, especially when the wind is blowing, which it did Thursday, 2 June.  We estimate age at 30-35 days by seeing more feathers emerging from its sheaths.  The cere and feet are getting lemony in color as well.  We still see the little fluffy head peer from around the pine boughs that are still being brought into the nest.  We haven’t seen the adult bring any prey to the nest.  It comes in, checks on things, then leaves, spending less than 1 minute at the nest.  It was so windy on the 2nd of June it was hard to keep the scopes still.  There was a lot of ‘floating’ on the thermals activity too.  A couple of times an adult would ‘float’ right by the nest, then land.  One adult landed in the nest, followed immediately by the other, who arrived with vocalization, causing the other to flee.  The 2^nd adult appeared to be larger, so it appears it was the female, who caused the male to leave.  The chick appears to be quite hungry.  The crop is very flat.  We did see them soaring around the nest, checking it out, a few times today.  No pine bough or prey was delivered to the nest though.  There was no self-feeding either visit this week and we didn’t see the chick being fed.  Compared to last week, this was a very quiet week, except for the chirping nestling.”

I’m looking forward to getting back out into the field next week and receiving weekly reports from our Posse teams. I hope the roads dry out a bit–we expect our first eaglets to leave the nest in the next 7 – 10 days.

Eaglets from Nest 23A eat a rabbit Leg, 2010

Eyrie notes from July 19, 2010

Dr. Charles R. Preston, Senior and Founding Curator at the Draper Museum of Natural History, Buffalo Bill Historical Center in Cody, Wyoming

19 July – There are still several eagle youngsters in the nest or hanging around the nest for shelter and continued feeding.  Richard Jones and I visited several nests last week and found that some young eagles that had fledged several days ago were back on the nest ledge, under rocky outcrops for shade.  Temperatures soared to 100 degrees F in the Bighorn Basin, so shade was popular and critical especially to youngsters who may have trouble with thermoregulation!

Eyrie notes from July 12, 2010

Dr. Charles R. Preston, Senior and Founding Curator, Draper Museum of Natural History at the Buffalo Bill Historical Center in Cody, Wyoming

12 July – Vegetation in the Bighorn Basin is beginning to turn brown and crunchy, now, and most wildflowers have passed peak bloom.  You can really pick out patches of cheatgrass in some areas.  This alien, invasive species thrives in disturbed ground and can create real problems for wildlife and livestock grazing if it takes over too much landscape.  It dries early in the season and invites the spread of wildfire.  After wildfire, it often outcompetes native grasses and forbs, and thus takes over even more ground.  Bureau of Land Management, Park County Conservation, and several conservation groups are working to reduce cheatgrass in the Basin, but it is a tough job because of so much disturbed land around human activity.

Eyrie notes from July 6, 2010

Dr. Charles R. Preston, Senior and Founding Curator, Draper Museum of Natural History At the Buffalo Bill Historical Center in Cody, Wyoming

06 July – Summer seems to have disappeared after only a week or so! Today, we have rain, with high temps in the 50s. Many of our birds are beginning to successfully fledge, and a few have left their nests before being able to fly.

Eyrie notes from June 28, 2010

Dr. Preston asnwers questions for field trip attendees on Saturday

Dr. Charles R. Preston, Senior and Founding Curator, Draper Museum of Natural History At the Buffalo Bill Historical Center in Cody, Wyoming

28 June – Summer has finally arrived in the Bighorn Basin!  Temps have climbed to 90 degrees plus for a couple of days, now, and vegetation is beginning to fade.  Last week, however, was peak blooming period for larkspur and globemallow in much of the Basin.  Pronghorn fawns were seemingly everywhere last week.  A few of our Golden Eagles have now fledged, and I expect several more to leave the nest during this week.  We’ll know more after Richard completes his aerial survey later this week.

Nest 23 Golden Eagle Chicks, 2010